In one type of prior art hearing aids the electronic components are fastened to a circuit board whereon the electric leads, which interconnect the electronic components are printed and the circuit board is then fastened to the structural parts of the hearing aid. The circuit board can be either rigid or flexible. The use of a circuit board makes placement and fixation of the electronic component easy and straightforward, and it can be done in automated processes. The problem is that the circuit board takes up space in the hearing aid or headset, and as small size audio devices are in high demand by the users this is a sever problem.
In another type of prior art hearing aids the circuit board is at least partially substituted with thin wires. The use of such wires is highly undesirable, because trained personnel must carry out fastening of the wires to the components by hand. This makes the resulting hearing aid expensive to manufacture and the hand operation is prone to a high rate of errors.
It is known in electronic devices to provide electric leads directly on non-flat polymer surfaces. This is done by firstly marking traces and areas for the leads by laser light in order to change the structure of the polymer surface. Thereby it becomes possible to adhere layers of metal to the marked traces and areas and in this way electric leads may be formed directly on the polymer surface. The process is known under the name of 3D-MID: Moulded Interconnect Devices. Electronic components may then be placed on the surface and through a usual re-flow soldering process gain electric connection with the leads and physical good connection with the surface. It has previously not been seen as an advantage to use this technique in connection with the production of hearing aids.